The Collaborative International Dictionary of English v.0.48:

Chaetognath \Ch[ae]"tog*nath\, a. (Zool.)
   Of or pertaining to the Ch[ae]tognatha.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

chaetognath \chaetognath\ n.
   any worm of the Chaetognatha; transparent marine worm with
   horizontal lateral and caudal fins and a row of movable
   curved spines at each side of the mouth.

   Syn: arrowworm.
        [WordNet 1.5] Chaetognatha

WordNet (r) 3.0 (2006):

chaetognath
    n 1: any worm of the Chaetognatha; transparent marine worm with
         horizontal lateral and caudal fins and a row of movable
         curved spines at each side of the mouth [syn: arrowworm,
         chaetognath]